In this research programme, the "host-protective antigens: of two natural and highly successful parasites of mice, Giardia muris and Taenia taeniaeformis will be identified and isolated. G.muris trophozoites and T.taeniaeformis oncosheres are known to contain antigens capable of inducing host-protective immunities: BALB/c (but not C3H/He) mice can be protected against G.muris infection by injection of trophozoites in Freund's complete adjuvant; all mouse strains can be protected against T.taeniaeformis infection by infection of oncospheres in strong adjuvants. Parasite antigens radiolabeled by biosynthetic and extrinsic labeling methods will be immunoprecipitated and analysed by one and two-dimensional electrophoretic techniques. Affinity chromatography on antibody and lectin absorbents will be used to isolate antigens to be incorporated into defined antrigen vaccines. Attempts will be made to determine why some adjuvants are better than others for induction of vaccine-based host-protective immunity. In addition, with isolated parasite antigens, comprehensive analysis will be performed on the location, magnitude and nature of specific antiparasite immune responses in susceptible and resistant mice.